An implementation issue (arguably a bug) in how nginx 1.9.x+ negotiates connections, and OkHttp's failure to recover from it, currently prevent the Android app from logging in or editing over an HTTP/2 connection. We've worked around this for the time being by forcing OkHttp to use HTTP/1.1. Meanwhile, nginx is working to modify this behavior and OkHttp is working on a patch to gracefully recover from the connection failure, to be included in the next release (3.3). We should monitor both so that we can benefit from HTTP/2 when a fix is released.
And related bugs triggered by the HTTP/2 rollout:
T134758: [BUG] Unable to load Edit preview, and thus unable to save edit.
T134759: [BUG] Unable to log into the app.